The present invention is generally concerned with the enhanced recovery of crude petroleum for subsequent refining, distillation or the like. More particularly, the present invention is concerned with a chemical method which broadly employs fatty acids for extracting petroleum by reducing its viscosity, but which further contemplates the recycling of the fatty acid reactant.
As will be immediately recognized by those skilled in the petroleum arts, the broad science of secondary recovery has long contemplated the further extraction of petroleum crude from "dry" wells by the injection of various solvents, high pressure steam, or other chemicals. A variety of prior art attempts have been proposed for secondary recovery. A typical example includes the drilling of a plurality of radially spaced apart secondary shafts surrounding the primary well, into which high pressure steam is injected to force out petroleum residue.
The term oil shale refers to a hard carbonaceous rock that can produce oil when heated to pyrolysis temperatures of approximately 800.degree. to 1000.degree. F. Petroleum is recovered when the shale is properly subjected to a suitable solvent. The oil precursor in such rock is a high molecular weight organic polymer called Kerogen.
Kerogen obtained from the upper regions of the Colorado and Utah oil shales has an average composition, by-weight, as follows: Carbon (80.5%); Hydrogen (10.3%); Nitrogen (2.4%); Sulpher (1%); Oxygen (5.8%). The host rock may consist mainly of Dolomite, Calcite, Quartz and other clays. The oil shale area of most significance in the United States is the Green river formation of Colorado, Utah and Wyoming. While a small percentage of this oil shale may be mined by surface techniques, most of it will be recovered through underground mining in large room-and-pillar mines.
Major emphasis has recently been directed to both underground mining and above ground retorting of minerals and oil shale. A variety of heat treating processes have been developed and reported in the prior art for developing and recovering suitable petroleum extracts from both tar sands, kerogen, and subterranean "dry" wells.
In the prior art it is well known to subject such petroleum bearing formations, wells or the like, to an organic solvent such as a fatty acid. Such an acid tends to reduce the viscosity of the captured petroleum, facilitating subsequent pumping. Fatty acids such as carboxylic long chain or aliphatic acids have been previously employed in the prior art. Moreover, such processes have been combined with the injection of high pressure steam to promote a subsequent aqueous reaction.
By using long chain carboxylic acids, productivity increases of as much as 50% or more have been obtained. The inherent economics of such a situation have yet to favor its large scale application, mainly as a result of the initial cost of the presently non-recycled fatty acids. Moreover, typical crude petroleum, once contaminated with the fatty acid in solution, cannot be purified by standard retorting, distilling or the like since the contaminating fatty acid will form an azeotrope with nearly every fraction of the desired petroleum oil. For this reason virtually every major oil refinery will refuse raw crude if substantially contaminated with fatty acid(s).
Formations of oil sands are usually shallow enough to allow for their removal by standard surface mining techinques. After the outcrop is suitably mined and the recovered petroleum bearing rock transported to a processing (i.e. crushing) position, treatment of the recovered sands etc. within an agitation tank may proceed by subsequent mixture with a fatty acid in aqueous solution. Agitation or heat may be additionally applied to lower the viscosity of the resulting solvated oil depending upon the temperature at which extraction is carried out. Silica and other minerals yielded in this manner may be separated by gravity through use of a centrifuge or the like. Electrolytes such as sodium cloride or potassium cloride have been added previously to sharpen this separation process. However it would seem desirable to initially separate the bitumen in the very first step to enhance the efficiency of a secondary oil recovery system. Moreover, due to the costs of the extraction solvents, some form of system for providing continuous recirculation and recycling of same is mandated.
In the prior art the use of heavy aliphatic hydrocarbon acids and the like, including oleic acid and its derivatives, is known in secondary oil recovery. Moreover saponification reactions have previously occurred in conjunction with crude oil recovery systems as a by-product between the basic substances employed. Separation by the step of precipitation is also well known. U.S. Pat. No. 3,075,918 teaches the use of carbon dioxide in conjunction with the secondary recovery of hydro-carbon fuels. Specifically, it has been suggested to employ carbon dioxide in combination with the odixes of alkaline earth metals, the reaction yielding carbonates thereof. Kennedy U.S. Pat. No. 2,164,459 teaches secondary recovery in which oil and fatty acids or other emulsifying agents are employed. The latter reference points out the use of oleic compounds, and discusses the concept of saponification. U.S. Pat. No. 2,233,382 teaches a great deal of useful background information concerning the use of relatively high molecular weight acids in the secondary petroleum recovery arts. The latter patent, while it suggests the natural occurrence of soap-like derivatives as a result of the reaction of alkaline substances, is primarily directed towards the use of esters and related compounds in secondary recovery. U.S. Pat. No. 4,224,138 is directed to the recovery of tar sand subsequently subjected to a recovery process. The latter reference teaches the use of chemicals such as sodium hydroxide and/or other monoalkaline reagents for the removal of bitumen prior to separation of the slurry. U.S. Pat. No. 4,172,025 teaches the use of caustic soda to provide a slurry reaction. Other less relevant art known to us includes U.S. Pat. Nos. 3,392,105; 4,133,381; 2,342,106; 4,172,025 and 4,116,809.